# Read MAT and LUD Files Using Fortran

Read the .mat file that contains the elements of the MoM matrix A and the .lud file that contains the LU decomposition of the method of moments matrix A.

The .mat and .lud files are binary files, written in the native platform coding (for example, little-endian coding on the INTEL / AMD CPUs), and have a Fortran block structure using the COMPLEX data type (in either single or double precision).

```
CHARACTER MD5_CHECK*32
INTEGER VERSION
LOGICAL FILE_SINGLE_PRECISION
INTEGER ROWS, COLUMNS
INTEGER I, J
OPEN (19, FILE="filename", FORM='UNFORMATTED')
READ (19) VERSION
READ (19) MD5_CHECK
IF (VERSION.GE.2) THEN
READ (19) FILE_SINGLE_PRECISION
ELSE
FILE_SINGLE_PRECISION = .FALSE.
END IF
READ (19) ROWS
READ (19) COLUMNS
DO J=1, COLUMNS
IF (FILE_SINGLE_PRECISION) THEN
READ (19) (MATRIX_S(I,J), I=1, ROWS)
ELSE
READ (19) (MATRIX(I,J), I=1, ROWS)
END IF
END DO
CLOSE (19)
```

with
these additional variables:- MATRIX
- a two dimensional array at least ROWS*COLUMNS in size to store the data in double precision (declared as DOUBLE COMPLEX).
- MATRIX_S
- a two dimensional array at least ROWS*COLUMNS in size to store the data in single precision (declared as COMPLEX).

` READ (19) (MATRIX_S(I,J), I=1, ROWS)`

reads a
complete column of the matrix at once.## File Structure

```
| length=4 | VERSION (4 bytes) | length=4 |
| length=32 | MD5_CHECK (32 bytes) | length=32 |
(| length=4 | FILE_SINGLE_PRECISION (4 bytes) | length=4 |) -- Only present if VERSION >= 2
| length=4 | ROWS (4 bytes) | length=4 |
| length=4 | COLUMNS (4 bytes) | length=4 |
| length=ROWS*es | MATRIX(:,1) (ROW*es bytes) | length=ROWS*es | -- es is 8 or 16 bytes depending on precision.
| length=ROWS*es | MATRIX(:,2) (ROW*es bytes) | length=ROWS*es |
...
| length=ROWS*es | MATRIX(:,COLUMNS) (ROW*es bytes) | length=ROWS*es |
```

Here
each record of interest is preceded by a length field that indicates the size (in
bytes) of the record.When reading these files using an external utility, such as one written in C or MATLAB, these length fields must also be considered. They can either be ignored or can be used to detect errors in the reading process.